In recent years, a storage apparatus such as a magnetic disk apparatus which can read and write data has been developed. When data is read from a magnetic disk, the magnetic disk apparatus reads a written signal required to read data from a track written in the magnetic disk apparatus. In general, in the magnetic disk apparatus, the written signal is read by a read head required to read the written signal. The read head is independent of a write head used upon writing data.
It is demanded to write many data on the magnetic disk by writing tracks on the magnetic disk at a high density. At this time, since the tracks are written at a high density, the read head is required to be positioned at high accuracy. For this reason, the read head position where the written data can be read with the best quality is required to be adjusted in advance with respect to the read head position upon data writing. The written data has to be read at that read position. However, due to a deviation of a write position in an actual write/read operation, a read error often occurs even at the adjusted position of the read head which can read data with the best quality. When the read error occurs, the read position of the read head is corrected with respect to a written signal and the written signal is repetitively read by read retry processing until the written signal can be read.
However, when the read position of the read head is repetitively corrected, a processing time required to read the written signal is prolonged, thus lowering data read performance. When a plurality of tracks are written on the magnetic disk while they partially overlap each other, a practical track width from which the written signal can be read is often narrowed down. Even in such case, it is demanded to read the written signal without lowering the performance.